The present invention relates to devices and methods for remote, selective blocking of a cold steam used in crystal annealing during X-ray protein crystallography.
At the Advanced Photon Source, a national synchrotron radiation research center located at the Argonne National Laboratory near Chicago, Ill., a number of facilities exist for using diverted intense X-ray beamlines for visualization of an object using X-ray diffraction. One such use is for X-ray protein crystallography, i.e., the visualization of protein molecule crystals using X-ray diffraction. During X-ray protein crystallography, the technique of crystal annealing is performed. Crystal annealing includes warming a frozen protein crystal to room temperature, and then re-freezing it. This may allow the crystal to freeze more perfectly, and is commonly used to either rescue a poor initial freeze (e.g., one with ice rings that interfere with structural visualization of the protein) or to improve the diffraction properties of the frozen crystal. Two common techniques for performing crystal annealing involve either 1) re-introducing the crystal into cryoprotectant, or 2) merely blocking the stream of cold nitrogen gas which keeps the crystal frozen.
This second technique is generally preferred because of its simplicity. Traditionally, the cold stream is manually blocked by inserting a card such as a credit card between the crystal and the cold stream for a few secondsxe2x80x94until one can see the liquid around the crystal in the loop thawxe2x80x94then removing the card. This manual blocking technique with a credit card has been satisfactory, but because there is not much room around the crystal in the setups used for protein crystallographic X-ray data collection, the crystal is frequently hit during the process, sometimes destroying the crystal.
This manual blocking technique requires the user to be in close proximity to the X-ray machine, but because of the high radiation levels of the emitted X-ray beams, the user can""t be in close proximity to the X-ray machine while the X-ray machine is in use. As a result, the user must be sufficiently isolated from the intense X-rays emitted during X-ray crystallography, and must stop X-ray emission and undergo a time-consuming X-ray setup entry and exit process every time the user wants to perform the manual, cold-stream blocking technique during crystal annealing. Not only is the user limited in the amount of time that can be spent at the shared facility where X-ray protein crystallography is performed because of the high demand for the facility, but the hourly rental rate for the facility is expensive, currently renting at approximately $2000/hr. Thus, the time-consuming entry and exit process required every time one wants to manually block the cold stream increases the amount of time spent on crystal annealing and, hence, increases the amount of time spent performing X-ray protein crystallography.
Thus, a need exists for a way to block the cold stream used in crystal annealing during X-ray protein crystallography that solves one or more of the problems of the past.
The present invention includes a remote-control blocking mechanism to block the cold stream used in crystal annealing during X-ray protein crystallography that eliminates the aforementioned problems, including eliminating the danger of physically disturbing the crystal.
In an aspect of the invention, a blocking device for remote selective blocking a cold stream used in a protein crystal annealing process during X-ray protein crystallography includes a blocking member adapted to be selectively moved between at least a blocking position where the blocking member blocks the cold stream and a non-blocking position where the blocking member does not block the cold stream, and an actuation mechanism adapted to impart movement to the blocking member to cause the blocking member to be selectively moved between at least the blocking position where the blocking member blocks the cold stream and the non-blocking position where the blocking member does not block the cold stream. In a preferred implementation, the actuation mechanism includes a remotely located switch for controlling selective blocking of the cold stream from a remote location. In another implementation, the actuation mechanism includes a timer in place of, or in addition to, the remotely located switch.
Another aspect of the invention involves a method of remote, selective blocking of a cold stream used in a protein crystal annealing process during X-ray protein crystallography. The method includes providing a remotely actuatable blocking device adjacent the cold stream, the blocking device including a blocking member adapted to be selectively moved between at least a blocking position where the blocking member blocks the cold stream and a non-blocking position where the blocking member does not block the cold stream, and an actuation mechanism adapted to impart movement to the blocking member to cause the blocking member to be selectively moved between at least the blocking position where the blocking member blocks the cold stream and the non-blocking position where the blocking member does not block the cold stream; and actuating the actuation mechanism from a remote location to impart movement to the blocking member to cause the blocking member to be selectively moved between at least the blocking position where the blocking member blocks the cold stream to allow the protein crystal to be warmed and the non-blocking position where the blocking member does not block the cold stream to allow the protein crystal to be cooled.
These and further objects and advantages will be apparent to those skilled in the art in connection with the drawing and the detailed description of the preferred embodiment set forth below.